Components in a gas turbine engine are often cooled to survive the high temperatures found therein. One method used is thin film cooling by a supply of air, used as a cooling fluid, which is provided to a passage within the component, exiting via cooling holes to form a thin film over the external surface of the component. In addition to removing heat from the component by conduction, the thin film of cooling air serves to prevent hot gas within the gas turbine engine impinging upon the component.
The cooling air used for thin film cooling must be supplied at a pressure greater than the gas path pressure in which the component is operating. This requires work to be carried out on the cooling air, representing a loss of useful power from the engine. In some examples, machining or laser drilling may be used to form films holes having consistent diameters for thin film cooling.
In some examples, film cooling holes are shaped to reduce the use of cooling air. In one example, a shaped cooling hole may be a 2D diverging hole exiting at low incidence to the surface of the component to be cooled. This “fan” shaped hole allows the cooling film to form more readily than would a conventional constant-bore hole. Such cooling “fan” shaped holes may be manufactured using EDM spark erosion, or, more recently by laser drilling.